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Biology II
DIGESTIVE SYSTEM
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FUNCTIONS OF THE DIGESTIVE SYSTEM
Ingestion The taking in of food.
Digestion Physical and chemical breakdown of
food into smaller molecules.
Absorption Movement of nutrients into the
bloodstream.
Defecation Removal of indigestible waste.
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MOUTH ANATOMY
Three pairs of salivary glands empty secretions intothe mouth
1. Parotid glands
2. Submandibular glands
3. Sublingual glands
Functions of saliva:
Dissolves chemicals in food so they
can be detected by the taste buds.
Moistens food so that it can be swallowed.
Contains salivary amylase, a digestive enzyme.
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DIGESTION IN THE MOUTH
There are two types of digestion:
Mechanical digestion, which is the physical process
of breaking food into smaller pieces.
Chemical digestion, when enzymes catalyze
chemical reactions that lead to the breakdown of
food molecules.
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DIGESTION IN THE MOUTH
Mechanical digestion in the mouth occurs throughmastication, or the chewing and grinding of food by
the teeth.
Chemical digestion occurs when salivary amylase
catalyzes the breakdown of starch (polysaccharide)into maltose (disaccharide).
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Teeth
(Incisors)
Hard Palate
Soft Palate
Uvula
Tongue
Frenulum
Palatine
Tonsils
Palatal
Arches
Vestibule (betweenlower lip and gingiva)
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TEETH
The outermost layer of the tooth is enamel. Made of calcium phosphate, the hardest biologically-made
substance.
Most of the inner tooth is dentin, which is similar to
bone except without any living cells.
The living cells of the tooth are located in the pulp
cavity.
All blood vessels and nerves into this cavity come through
the root canals at the base of the tooth.
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Crown
(Enamel)
Pulp Cavity
Gingiva
Bone Tissue
(Mandible)
Root
Canal
Dentin
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TOOTH DISORDERS
Cavities orcaries occur when
naturally-occuring bacteria withinthe mouth overgrow due to thepresence of food particles.
The bacteria produce acid as a wasteproduct, which dissolves the calciumphosphate enamel.
If cavities are allowed to becometoo deep, a root canal will cleanout and dissolve all the tissue in the
pulp cavity, leaving an antibioticpaste behind.
The tooth no longer has any living cellsat this point.
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TYPES OF TEETH
Incisors are blade-shaped teeth at the front of themouth.
Clipping or cutting.
Cuspids (canines) are cone-shaped with a pointed
tip.
Tearing or slashing.
Bicuspids and molars have flattened tops.
Crushing, mashing, or grinding.
Wisdom teeth are an additional set of molars that
often develop in locations where they cannot erupt.
Vestigial structures.
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Incisors
Cuspid
Bicuspids
Incisors
Cuspid
Bicuspids
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PHARYNX
Food is formed into achewed,moistened ball called a bolus.
The bolus is pushed back toward
the pharynx with the tongue.
While swallowing, all
passageways except to the
esophagus are blocked.
The uvula moves backwards,
blocking the nasal cavity.
The epiglottis folds down, blocking
the trachea.
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ESOPHAGUS
The bolus movesthrough the
esophagus by a
series of smooth
muscle contractionscalled peristalsis.
The bolus
eventually enters
the stomachthrough the cardiac
sphincter.
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Esophagus
Fundus
CardiacSphincter
Lesser
Curvature
Greater
Curvature
Body (Rugae)
Pyloric
RegionPyloricSphincter
Duodenum
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STOMACH
The stomach is a muscular organ made of foursections:
Cardiac Region closest to the esophagus and heart.
Fundus Superior bulge in stomach.
Body Middle section Pyloric Inferior region, closest to the small intestines.
The stomach has internal folds called rugae, thatincrease the surface area for digestion.
The innermost lining of the stomach is simplecolumnar epithelium.
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STOMACH
The cardiac sphincteris a ring of smooth
muscle intended to allow
food into the stomach,
but not out. Exceptions include
vomiting, heartburn, acid
reflux.
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STOMACH
Presence of food in the stomach stimulates the releaseof the hormone gastrin.
Gastrin causes the stomach glands to produce:
Pepsinogen, an inactive enzyme produced by chief cells.This converts to pepsin, an active enzyme that breaks downproteins into amino acids.
A layer ofmucus to protect the stomach from being dissolvedor digested.
Hydrochloric acid lowers the pH of the stomach contents,
which activates pepsin. This is produced by parietal cells. No absorption occurs in the stomach, except for aspirin
and alcohol.
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Mucus
Cells
RugaeChief
Cells
Parietal
Cells
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STOMACH-INTESTINES
The partially digested food is now referred to aschyme.
The stomach will release small amounts (30mL) of
chyme into the small intestine at a time through the
pyloric sphincter.
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SMALL INTESTINES
The first section ofthe small intestines
is the duodenum.
This is where most
of the actual
digestion occurs.
Digestive secretions
from the pancreas
and liver (gallbladder) are both
sent here.
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Falciform Ligament
Liver
Duodenum
Gall Bladder
Pancreas
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DUODENUM
The pancreas releases bicarbonate and enzymes
into the duodenum:
Bicarbonate neutralizes the stomach acid, stopping the
action of pepsin..
Pancreatic amylase (starch maltose)
Lipase (Lipids Fatty acids)
Nuclease(DNA / RNA Nucleotides)
Trypsin(Protein Amino acids)
The liver releases bile, which separates fats intosmaller droplets to increase the rate of digestion by
lipase.
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JEJUNUM-ILEUM
Food is moved throughthe small intestine by
peristalsis, just like in
the esophagus.
Absorption of the end-products of digestion
occurs all along the
jejunum and ileum.
Villi are present in all cells
along the intestines to
increase the surface area
for absorption.
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JEJUNUM-ILEUM
Active transport movesthe substances
(monosaccharides,
amino acids, fatty acids,
etc) across the cells of
the intestines into theblood.
Substances are then
transported to the liver
by the hepatic portal
vein.
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LARGE INTESTINE
The beginning of the large intestine is the cecum. The appendix is attached here.
Three segments of the large intestine:
Ascending colon
Transverse colon
Descending colon
Ends with the rectum.
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Oral Cavity
Sublingual GlandSubmandibular
Gland
Esophagus
Parotid Gland
UvulaTongue
Pharynx
Trachea
Diaphragm
SpleenLiver
Stomach
Pancreas Transverse ColonDescending Colon
Jejunum
Sigmoid Colon
Rectum
Anus
Ascending Colon
ileum
Appendix
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LARGE INTESTINE
No digestive enzymes are present here. Bacteria that reside in the large intestine digest some
of the remaining nutrients, producing vitamins K, B,
and some gases.
Water and vitamins are absorbed, while theremaining material is eliminated as feces.
Undigested food residue
Mucus
Bacteria
Water
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LARGE INTESTINE
Movement through the largeintestine is slow, but powerful.
Peristalsis occurs 3-4 times per day.
A buildup of feces in the rectum
causes the defecation reflex. The internal anal sphincter (involuntary
smooth muscle) is relaxed.
The external anal sphincter (voluntary
muscle) must be relaxed beforedefecation can actually occur.
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ACCESSORY ORGANS
The pancreas, in addition to producing digestiveenzymes, also controls blood sugar.
Islets of Langerhans contain the cells that actually
produce these hormones.
Insulin Stimulates the absorption of glucose from bloodand production of glycogen for storage.
Glucagon Stimulates the breakdown of glycogen into
glucose, raising blood sugar.
The liver, in addition to making bile, detoxifies anypoisons absorbed by the digestive tract.
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APPENDIX
The appendix is a small dead-end tube connected tothe beginning of the ascending colon.
The appendix is believed to be a vestigial structure. It used
to be a larger cecum an organ that herbivores use to
ferment and digest cellulose.
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CONNECTIVE TISSUE
The stomach is held in place with the otherabdominal organs by the greater and lesser
omentum
The intestines are held together by mesentary.
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MUMPS
A viral infection that causespainful swelling of the salivary
glands, especially the parotid
gland.
Airborne and highlycontagious.
Can be vaccinated against.
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HEARTBURN
Influx of stomach acid into the esophagus. Can be the result of excessive acid production in the
stomach, or a faulty cardiac sphincter.
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PEPTIC ULCERS
An erosion of the innerstomach or duodenum lining.
Causes include:
Inflammation from bacterial
infection.
Certain painkillers (aspirin,
ibuprofen) can inhibit the
production of stomach mucus.
Stress (not fully understood why)
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VOMITING
There are multiple sources ofstimulation that can lead to
vomiting.
Irritation of the gastrointestinal
tract.
Irritation of the pharynx (gag
reflex)
Multiple trigger zones in the brain.
The actual process of vomitinghas several physiologic steps.
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VOMITING
Salivary glands increase production of saliva toprotect teeth from acid erosion.
A deep breath is taken to prevent aspiration.
Inhalation of foreign substances, such as vomit, can lead to
serious respiratory infections like pneumonia.
Retroperistalsis (reverse peristalsis) sweeps the
digestive tract contents through a relaxed pyloric
sphincter, into the stomach.
Abdominal muscles contract, cardiac sphincter
relaxes, and contents exit through the esophagus.
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DIARRHEA
Diarrhea is the presence of abnormally loose orliquid feces.
There are multiple types of diarrhea, all of which are
caused by an excess of water inside the intestines.
Some bacteria (Cholera, E. coli O157:H7) produce a toxinthat creates an ion imbalance in the intestines. This results
in an osmotic flow of water into the intestines.
Laxatives often contain an ion (like magnesium) that will
intentionally create an osmotic imbalance.
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LACTOSE INTOLERANCE
People that are lactose intolerant donot produce the lactase enzyme.
The gene that produces this enzyme shuts
off after infancy, when breastfeeding ends.
Undigested lactose eventually reachesthe large intestine, causing an osmotic
imbalance (diarrhea).
Bacteria are able to ferment the
lactose, producing excessive amountsof gas.
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DIABETES
The pancreas stops producing or does not produceenough insulin, resulting in high blood sugar levels.
Type I Diabetes is the result of the immune system
destroying the insulin-producing cells of the pancreas.
No insulin is produced. The patient is dependent on insulininjections.
Type II Diabetes occurs when there is an insulin
deficiency in the body, or the cells do not respond
properly to insulin. Most common cause is obesity.
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